The present invention relates to an electronically stabilized tracking system and more particularly to such a system using a beam-steerable radar configuration.
Since the advent of radar, numerous applications of radar, both military and commercial, have been developed, particularly in the field of avionics. Until recently, however, airborne radars across diverse applications have typically shared the common feature of the radar antenna being inertially, or "gyroscopically", stabilized using mechanical means such that operation of the radar is not affected by movements of the aircraft. Such mechanical stabilization entails a set of common mechanical problems including wear, failure, and involved repair. Of late, radars have been developed that do not rely on moving parts, i.e., are not mechanical but operate wholly electronically. In order to provide stabilization as was previously provided mechanically, correction factors related to aircraft motion have been applied to radar returns downstream of the radar receiver itself. Such correction is not easily achieved and encounters serious difficulties when real-time decisions and responses are to be made based on the radar returns.
The present invention is directed toward providing radar beam stabilization at the beam itself and will find widespread use in applications involving tracking of a multiplicity of objects as, for instance, in collision avoidance systems and applications involving tracking of a single object as in homing devices and seekers. For simplicity, the present invention will be described in the context of a homing device tracking a single object, more particularly an electronically stabilized "strapped down" seeker for a guided weapon. From the following description, application of the present invention to situations involving tracking of a multiplicity of targets will become apparent.
The function of a seeker in a guided weapon system is to track the position of a moving target in much the same fashion as a human observer would, training its "sight" on the target and following the target's motion with its "head" in two dimensions, up/down and left/right. The sight of the guided weapon is typically provided by radar, and motion of a radar antenna in two dimensions has typically been achieved by mounting the antenna in a set of gimbals.
Although such an arrangement is common, it is not without drawbacks. The gimbal has associated with it significant inertia, tending to make tracking of the target sluggish. Furthermore, the mechanical nature of the gimbal with its moving parts renders it susceptible to wear, inaccuracy and failure.
Recent advances in millimeter wave technology have led to the development of beam-steerable "strapped down" seekers using phased-array antennas. The radiated beam of such an array may be scanned electronically by controlling the excitation phase of individual elements without the need for any moving parts. Although strapped down seekers present an attractive alternative to gimballed seekers, attempts at strapped down guidance have not been fully successful. Rather, strapped down guidance has always been regarded as high risk for precision guided weapons.
An object of the present invention, then, is to provide an electronically stabilized tracking system.
Another object of the present invention is to improve control of a guided weapon system using a strapped down seeker.
Another object of the present invention is to eliminate potential instability in a guided weapon control system using a strapped-down seeker.
A further object of the present invention is to eliminate adverse effects of body coupling in a strapped down guidance system.
A still further object of the invention is to provide an electronically gimballed, inertially stabilized strapped down seeker implementation.